1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and an apparatus for transmitting uplink control information in a wireless communication system.
2. Related Art
In a wideband wireless communication system, effective transmission and reception techniques and utilization measures have been proposed in order to maximize efficiency of limited radio resources. One of systems considered as a next-generation wireless communication system is an orthogonal frequency division multiplexing (OFDM) system that can attenuate an inter-symbol interference (ISI) effect with low complexity. In the OFDM, a data symbol input in series is converted into N parallel data symbols which are loaded on N separated subcarriers to be transmitted, respectively. The subcarriers maintain orthogonality in respect of a frequency. Respective orthogonal channels undergo independent frequency selective fading, and as a result, complexity in a receiver is decreased and an interval of transmitted symbols is increased to minimize inter-symbol interference.
Orthogonal frequency division multiple access (hereinafter, referred to as OFDMA) represents a multiple access method that implements a multiple access by independently some of usable subcarriers to each user in a system using the OFDM as a modulation scheme. The OFDMA provides frequency resources such as the subcarriers to each user and the respective frequency resources are independently provided to a plurality of users not to be overlapped with each other, in general. Consequently, the frequency resources are exclusively allocated for each user. In the OFDMA system, frequency diversity for multiple users may be acquired through frequency selective scheduling and the subcarriers may be allocated in various patterns according to a permutation scheme for the subcarriers. In addition, efficiency of a spatial area may be increased by a space multiplexing technique using multiple antennas.
Multiple-input multiple-output (MIMO) technology improves transmission and reception efficiency of data by using multiple transmitting antennas and multiple receiving antennas. A technique for implementing diversity in an MIMO system includes a space frequency block code (SFBC), a space time block code (STBC), cyclic delay diversity (CDD), frequency switched transmit diversity (FSTD), time switched transmit diversity (TSTD), precoding vector switching (PVS), spatial multiplexing (SM), and the like. An MIMO channel matrix depending on the number of receiving antennas and the number of transmitting antennas may be dissolved into a plurality of independent channels. The respective independent channels are called layers or streams. The number of layers represents a rank.
Uplink control information (UCI) may be transmitted through a physical uplink control channel (PCCH). The uplink control information may include various types of information including a scheduling request (SR), an acknowledgement/non-acknowledgement (ACK/NACK) signal, a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and the like. The PUCCH transports various types of control information according to a format.
In recent years, a carrier aggregation system attracts attention. The carrier aggregation system means a system that configures the wide band by collecting one or more subcarriers having a smaller bandwidth than a target wide band when the wireless communication system supports the wide band.
In the carrier aggregation system, a method for efficiently and reliably transmitting various types of uplink control information is required. In particular, when the periodic CSI (for example, CQI) and the ACK/NACK are simultaneously transmitted in the same subframe, it may be problematic by which scheme the transmission power is determined.